In spring 2009, I was invited to debate “torture” with Jon Stewart on “The Daily Show.” He gave me an opportunity to make a case with which he vehemently disagreed. He didn’t spout prepackaged sound bites — he presented thoughtful counterarguments. Not many television talk show hosts are willing — or able — to do that.

At one point, I suggested that if CIA interrogators should be regarded as war criminals for having waterboarded three al Qaeda commanders to make them reveal information that could save American lives, then surely President Truman should be regarded as a war criminal for dropping atomic weapons on Hiroshima and Nagasaki. Mr. Stewart said he agreed.

As soon as the segment ended, he leaned forward and whispered: “I can’t believe you got me to say Harry Truman was a war criminal.” A couple of days later, he went on the air and recanted. Kudos to him for that, too. However, he never explained the logic that led him to declare the CIA guilty and Truman innocent — indeed, a leader in good standing of “the greatest generation.”

Having pondered this since, here’s the best argument I can make for the Stewart Doctrine: During times of war, neither the laws of war nor any reasonable code of ethics prohibits killing enemies on the battlefield. But once an enemy has been captured and is in your custody, he’s your responsibility.

I think that’s right. Even Khalid Shaikh Mohammed, mastermind of Sept. 11 who also decapitated Daniel Pearl “with my blessed right hand,” should not be summarily executed or tortured as a form of punishment. What about using torture to uncover ongoing terrorist plots?

Mr. Stewart would say no, and I’d say he’s right. Here’s where the quarrel begins: You have to define torture. All rough treatment does not qualify. A red-hot poker through the eye, removing fingernails with pliers — that’s torture, no doubt about it.

How about solitary confinement, loud music and sleep deprivation? It depends. Among other things, you need to specify how long the subject would be made to endure such discomfort. To simply prohibit all such methods — known as “enhanced” techniques or, in an earlier era, “stress and duress” interrogation — makes neither legal nor ethical sense.

OK, so what about waterboarding, a practice that — let me reiterate — was used on only three “high-value” al Qaeda commanders? It had legal approval from the Justice Department and was not used after 2006 when Michael V. Hayden took over as CIA director.

In 2008, Christopher Hitchens, a man of the left, volunteered to be waterboarded. The headline of his Vanity Fair piece was widely quoted: “Believe Me, It’s Torture.” What almost no one quoted was his more nuanced conclusion that “a man who has been waterboarded may well emerge from the experience a bit shaky, but he is in a mood to surrender the relevant information and is unmarked and undamaged and indeed ready for another bout in quite a short time. When contrasted to actual torture, waterboarding is more like foreplay. On this analysis, any call to indict the United States for torture is therefore a lame and diseased attempt to arrive at a moral equivalence between those who defend civilization and those who exploit its freedoms to hollow it out, and ultimately to bring it down. I myself do not trust anybody who does not clearly understand this viewpoint.”

Exactly. Also relevant: The CIA didn’t waterboard as did the Japanese in World War II. Based on Department of Justice guidelines, American interrogators observed strict limits, and medical personnel was present to ensure no prolonged harm was done. In addition, all three waterboarded al Qaeda terrorists knew they could stop the sessions at any time. They simply needed to answer questions truthfully — to help save lives. One more thing: Waterboarding has long been used to train U.S. Special Forces. Do you think we’ve been torturing our own troops?

To Mr. Stewart and others I may not have persuaded: Let’s stipulate that waterboarding is torture. That begs the question: Is the Obama administration making a mistake by removing every other coercive technique from the CIA’s toolbox? Should an unlawful combatant really enjoy the same rights as an American accused of shoplifting — even if Americans will die as a result?

I can’t comprehend how that can be seen as serious policy in a time of war — which is what 2001-2003 was. And oh, by the way: The tide of war has not receded. Jihadi forces — including al Qaeda, the Islamic State and the Islamic Republic of Iran — are gaining ground.

Sen. Dianne Feinstein’s 6,000-page “torture report” offered not a single recommendation. I will: Let’s reconfirm that torture is prohibited. Let’s include waterboarding in that category. But then let’s initiate a rigorous and scientific study of the most effective interrogation techniques. Some, I’m confident, will be harsh.

The president, with congressional oversight, should decide which techniques will be permitted — always, sometimes and never. In fact, he should take the responsibility to approve the use of the toughest stress-and-duress techniques anytime there is a perceived need — just as he now approves the use of every drone attack.

George Orwell, a man of the left, is often attributed with pointing out that people sleep peacefully in their beds at night only because rough men stand ready to do violence on their behalf. Today, we are telling our rough men to stop being rough. It’s no longer necessary. It’s torture. It’s illegal and immoral. And we’re ashamed of them. To our enemies, this will appear as a kind of unilateral disarmament. All of us — Mrs. Feinstein and Mr. Stewart included — should think about that, perhaps tonight when we lie down in our beds.

• Clifford D. May is president of the Foundation for Defense of Democracies and a columnist for The Washington Times.